Brush sealing system and method for rotary machines

ABSTRACT

A rotary machine includes a rotary component disposed inside a stationary component. A brush sealing system is disposed between the stationary component and the rotary component. The brush sealing system includes a holding device coupled to the stationary component. A plurality of carbon bristles is provided, each bristle having a first end coupled to the holding device and a second end protruding from the holding device towards the rotary component. Diameter of each bristle is in the range of 0.1 to 1 mils.

BACKGROUND

The invention relates generally to a rotary machine and, more particularly, a sealing system for an interface between rotating and stationary components. As discussed below, certain embodiments of the invention include a brush sealing system for a rotary machine, and a method of operating a rotary machine for minimizing leakage of fluid during operating conditions of the machine.

Efficiency of rotary machines utilized for pumping a fluid, or compressing, or expanding a vapor (e.g. gas) depends upon the internal tolerances of the components comprising the machine. A loosely-toleranced rotary machine may have a relatively poor fit between internal components and may therefore exhibit poor efficiency, with relatively high leakage occurring within the device from regions of high pressure to regions of lower pressure. The traditional approach to this situation is to decrease the amount of clearance on these critical interfaces.

Sealing systems are used in rotary machines to reduce leakage of fluid flowing through the rotary machines. One or more seals extend along an interface between rotating and stationary components. For example, compressors and turbines may have one or more seals, e.g., labyrinth seals, at the interface between a series of rotating blades disposed within a casing or vane. These seals are intended to preserve a pressure differential across the rotating components, e.g., blades, between upstream and downstream sides of the rotary machine. In certain other examples, seals are also used in bearing sump systems to limit the amount of gas required to vent the sumps. The seals are usually subjected to relatively high temperatures, thermal gradients, and thermal expansion and contraction of the components during various operational stages. For example, the clearance can increase or decrease during various operational stages of the rotary machine. Typically, the labyrinth seal includes extra clearance to reduce the likelihood of contact and damage between the rotating and stationary components. However, the extra clearance also reduces the efficiency and performance of the rotary machine, because extra leakage occurs across the seal.

In another example, circumferential seals are used at the interface between the rotating and stationary components. Typically in a gas turbine engine, a plurality of stationary shroud segments are assembled circumferentially about an axial flow engine axis and radially outwardly about rotatable blade members, for example about turbine blades, to define a part of the radial outer flow path boundary over the blades. The circumferential seals facilitate maintaining tight clearance between the rotating and stationary components. However, circumferential seals generate higher interface temperatures leading to wear and larger clearance between the rotating and the stationary components. In yet another example, polymer brush seals are disposed between the rotating and stationary components. However, polymer brush seals generate higher interface temperature leading to wear and larger clearance between the rotating and the stationary components during transient operating conditions of the machine.

Accordingly, there is a need for a technique that reduces leakage of fluid in a rotary machine, and that maintains minimum clearance without impairing the performance of a seal during all operating conditions. In addition, a system for reducing leakage of fluid in a rotary machine during all operating conditions is also desirable. A plurality of carbon bristles are provided, each bristle having a first end coupled to the holding device and a second end protruding from the holding device towards the rotary component.

BRIEF DESCRIPTION

In accordance with one aspect of the present invention, a rotary machine includes a rotary component disposed inside a stationary component. A brush sealing system is disposed between the stationary component and the rotary component. The brush sealing system includes a holding device coupled to the stationary component. A plurality of carbon bristles is provided, each bristle having a first end coupled to the holding device and a second end protruding from the holding device towards the rotary component. The diameter of each bristle is in the range of 0.1 to 1 mils.

In accordance with another aspect of the present invention, a brush sealing system includes a holding device coupled to a stationary component. A plurality of carbon bristles are provided, each bristle having a first end coupled to the holding device, a second end protruding from the holding device towards a rotary component and configured to contact a rotary component to reduce leakage of pressurized fluid between the stationary component and the rotary component.

In accordance with another aspect of the present invention, a brush sealing system includes a holding device coupled to a stationary component. A plurality of carbon bristles are provided, each bristle having a first end coupled to the holding device and a second end protruding from the holding device towards the rotary component. Each carbon bristle has a friction coefficient less than or equal to 0.25, thermal conductivity greater than 8 watts per meter-Kelvin, and temperature capability greater than 700 degrees fahrenheit.

In accordance with another aspect of the present invention, a method of operating a rotary machine includes rotating a rotary component disposed inside a stationary component. A plurality of carbon bristles of a brush sealing system are contacted against the rotary component to reduce leakage of a pressurized fluid between the stationary component and the rotary component during operation of the machine; wherein diameter of each bristle is in the range of 0.1 to 1 mils.

DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIG. 1 is a diagrammatical view of rotary machine, e.g., an electrical generator including a plurality of brush seals in accordance with an exemplary embodiment of the present invention;

FIG. 2 is a diagrammatical view of a brush seal segment of a brush seal in accordance with the aspects of FIG. 1;

FIG. 3 is a diagrammatical view of a brush seal segment in accordance with aspects of FIG. 2;

FIG. 4 is a cross sectional view of a combination labyrinth/brush seal in a packing ring segment of a stationary component of a turbine sealing biased against a rotary component in accordance with an exemplary aspect of the present invention; and

FIG. 5 is a diagrammatical view of a brush seal in accordance with aspects of FIG. 4.

DETAILED DESCRIPTION

As discussed in detail below, embodiments of the present invention provide a rotary machine (for example, an electric generator, a gas turbine, or the like) in which a brush sealing system is disposed between a stationary component and a rotary component. The sealing system includes a holding device coupled to the stationary component. The exemplary sealing system includes a plurality of carbon fibers or bristles coupled to the holding device and configured to contact the rotary component. In accordance with aspects of the present invention, the parameters (such as friction coefficient, thermal conductivity, temperature capability, or the like) of the carbon fibers are chosen so as to maintain minimal clearances between the rotary component and the surrounding stationary component resulting in reduced fluid leakage and increased efficiency of the rotary machine. The bristle material also facilitates minimizing interface temperature between the sealing system and the rotary component during operation of the machine. Specific embodiments of the present invention are discussed below referring generally to FIGS. 1-5.

Referring to FIG. 1, a rotary machine 10 includes a brush sealing system 11 having two brush seals 12, 14. One of the brush seal 12 is shown in greater detail in the subsequent figures. In accordance with aspects of the present invention, the brush seal 14 is similar or generally identical to the brush seal 12, and the description of the brush seal 12 below also serves a description of the brush seal 14. In the illustrated embodiment, the rotary machine 10 is an electric generator. In other examples, without limitation, the rotary machine 10 may be a centrifugal compressor, or a steam turbine, or a gas turbine, or a bearing, or a sump, or the like. It may also be noted that the aspects of the present invention are not limited to an association with the rotary machine and may be associated with other machines subjected to fluid pressure drop during machine operation.

In the illustrated embodiment, the rotary machine 10 includes a stator 16, and a rotor 18 coaxially aligned with the stator 16. The rotor 18 is radially spaced apart from the stator 16 to define a gap 20 between the stator 16 and the rotor 18. Although in the illustrated embodiment, the stator 16 circumferentially surrounds the rotor 18, certain other applications require the rotor to circumferentially surround the stator as known to those skilled in the art. A fluid 21 is disposed in the gap 20 in such a way that the fluid 21 has a pressure drop generally transverse to the gap 20. The pressure drop is generated during operation of the machine 10. The brush seal 12 in accordance with aspects of the present invention includes a plurality of graphite or carbon bristles 22 configured to contact the rotor 18 to reduce leakage of fluid and also reduce temperature at a seal-rotor interface. The brush seal 12 is explained in greater detail with respect to subsequent figures below.

Referring to FIG. 2, the brush seal 12 includes a holding device 24 coupled to the stator 16. The plurality of carbon bristles 22 are coupled to the holding device 24. In accordance with aspects of the present invention, each carbon bristle 22 has a diameter in the range of 0.1 to 1 mils. Even though in the illustrated embodiment pertains to carbon bristles, aspects of the present invention may also be applicable to other non-metallic bristles. Typically, the bristles 22 are canted at an angle, for example, forty-five degrees angle. As known to those skilled in the art, the canting of bristles 22 improves the compliance of the seal with the rotor 18.

Referring to FIG. 3, brush 12 in accordance with an exemplary aspect of the present invention is illustrated. Each bristle 22 includes a first end 34 coupled to the holding device 24 and a second end 36 disposed proximate to the rotor 18. In certain exemplary embodiments, the second end of the bristle is configured to contact the rotor 18. In the illustrated embodiment, the holding device 24 includes a first plate 38, a second plate 40, and a matrix 42 disposed between the first plate 38 and the second plate 40. In certain exemplary embodiments, the first and second plates 38, 40 include a metallic material, or a composite material, or a combination thereof. The bristles 22 are clamped between the first and the second plates 38, 40. The first end 34 of each bristle 22 is coupled to the matrix 42 and the second end 36 protrudes from the plates 38, 40 towards the rotor 18. The matrix 42 may include epoxy, polyimide, or the like.

Typically, the conventional brush sealing system is configured to contact the rotor 18 thereby generating frictional heat at the seal-rotor interface during operation of the machine. The heat generated at the seal-rotor interface may be dissipated by convection, conduction through the brush seal, conduction through the rotor, or the like. When conventional brush seals are used, temperature at the seal-rotor interface increases, resulting in expansion of the rotor 18. The rotor expansion leads to higher interference between the brush seal and the rotor 18 causing brush seal wear and increased leakage of fluid between the rotor 18 and the stator. This reduces efficiency of the rotary machine.

The carbon bristles 22 in accordance with aspects of the present invention facilitates minimizing seal wear and maintaining temperature at the seal-rotor interface minimum. In certain exemplary embodiments, the brush seal 12 has the following parameters in order maintain a minimum temperature at seal-rotor interface. One effective bristle material of the brush seal has a friction coefficient less than 0.25, thermal conductivity greater than 8 watts per meter-kelvin (W/mK), and a temperature capability greater than 700 degrees fahrenheit. It should be noted that the values of the above mentioned parameters are exemplary values and should not be construed as limiting values. The combination of friction coefficient and thermal conductivity parameter of the bristle material of the brush seal 12 facilitates minimizing rotor expansion and ensuring adequate heat dissipation via conduction through the seal 12. The temperature capability parameter of the bristle material of the brush seal 12 facilitates minimizing seal wear resulting from higher temperature at the rotor-seal interface. In certain exemplary embodiments, the bristle material includes carbon or graphite. In certain other exemplary embodiments, the seal material may include other non-metallic material. In accordance with aspects of the present invention, the diameter of each bristle is maintained in the range of 0.1 to 1 mils so that a clearance of 0.1 mils may be maintained between the brush seal 12 and the rotor 18.

Referring to FIG. 4, a combination labyrinth/brush sealing system 44 in accordance with aspects of the present invention is illustrated. The sealing system 44 is disposed in a groove 46 of a stationary component 48 of a rotary machine 50 (for example, gas turbine). The sealing system 44 includes a packing ring segment 52 (labyrinth sealing element) disposed in the groove 46 of the stationary component 48. The packing ring segment 52 includes two sealing flanges 51 extending axially beyond a neck opening 54 of the groove 46. A hook flange 56 is configured surrounding the neck opening 54. As known to those skilled in the art, the groove 46 extends circumferentially along the stationary component 48. A rotary component (for example, a shaft) 58 is disposed inside the stationary component 48. It should be noted that although one packing ring segment 52 is illustrated, a plurality of packing ring segments may be configured similarly between the stationary component 48 and the rotary component 58. The packing ring segment 52 includes a plurality of tapered teeth 60 extending radially inward disposed proximate to, but spaced from recesses 62 formed on the rotary component 58 to form a labyrinth seal between the packing ring segment 52 and the rotary component 58.

An exemplary brush seal 64 is provided in the packing ring segment 52. The brush seal 64 in accordance with aspects of the invention includes a plurality of circumferentially extending array of carbon bristles 66 provided between a pair of side plates 68, 70. The side plate 68 extends short of the rotary component surface whereas the other side plate 70 forms a tapered tooth 69 similar to the tapered tooth 60 of the labyrinth seal. The tapered tooth 60 forms part of the labyrinth seal and also forms a backing plate at a low pressure side of the bristles 66. The tips of the bristles 66 are configured to contact the rotary component 58 forming a brush seal therewith. The brush seal 64 is provided in a groove, which extends circumferentially in the packing ring segment 52. In accordance with aspects of the present invention, each carbon bristle 66 has a diameter in the range of 0.1 to 1 mils. The carbon bristles 66 facilitate to minimize seal wear and maintain temperature at the seal-rotary component interface minimum. In certain exemplary embodiments, the carbon bristles have the following properties: strength-900 Ksi (kilopounds per inch squared), fiber modulus-19 Msi (Megapounds per inch squared), elongation-2%, service temperature-930 degrees fahrenheit, thermal conductivity-11.8 W/mK (watts per meter-kelvin). Smaller diameter of carbon bristles results in lower effective clearance at the seal-rotary component interface, and also lower stiffness resulting in lower heat generation. Greater strength of the carbon bristles results in greater stress capability. Higher thermal conductivity of the carbon bristles results in lower temperature at the seal-rotary component interface.

In certain exemplary embodiments, a plurality of springs may be provided between axially opposite flanges 51 of the packing ring segment 52 and the hook flanges 56 of the groove 46. The springs are configured to displace the packing ring segment radially outwards. Pressurized fluid may be introduced into the groove 46 via a passage 63 provided in the stationary component 48 for displacing the packing ring segment 52 radially inwards, for example, during steady state operating conditions of the rotary component 58 to effectively seal between high and low pressure regions 65, 67 respectively of the machine. In certain exemplary embodiments, the bristles 66 may be provided side-by-side along both circumferential and axial directions thereby providing a tortuous path between the bristles 66 for fluid flow between high and low pressure regions 65, 67 respectively of the machine.

Referring now to FIG. 5, the brush seal 64 in accordance with the aspects of FIG. 4 is illustrated. The brush seal 64 in accordance with the exemplary embodiment includes the plurality of circumferentially extending array of carbon bristles 66 provided between the pair of side plates 68, 70. As discussed previously, the side plate 68 extends short of the rotary component surface whereas the other side plate 70 forms the tapered tooth 69. One end 71 of the bristles 66 is coupled to a matrix 72 disposed between the side plates 68, 70. Other end 73 of the bristles 66 protrudes beyond the side plates 68, 70 towards the rotary component surface. The side plate 68 includes one flow channel 74 whereas the other side plate 70 includes a plurality of grooves 76. The flow channel 74 and the grooves 76 are configured facing the bristles 66. The flow channel 74 and the grooves 76 facilitate to provide pockets to reduce contact between the bristles 66 and the side plates 68, 70. In certain exemplary embodiments, the side plates 68, 70 include a metallic material, or a composite material, or a combination thereof. Pressurized fluid may be directed through the channel 74, grooves 76, and against the bristles 66 disposed between the plates 68, 70. The fluid deflects the bristles 66 towards the rotary component such that tip of the bristles contact the surface of the rotary component to maintain a seal thereagainst.

As discussed previously, in certain exemplary embodiments, bristle material of the brush seal 64 has a friction coefficient less than 0.25, thermal conductivity greater than 8 watts per meter-kelvin (W/mK), and a temperature capability greater than 700 degrees fahrenheit. The combination of friction coefficient and thermal conductivity parameter of the bristle material of the brush seal 64 facilitates minimizing rotor expansion and ensuring adequate heat dissipation via conduction through the seal 64. The temperature capability parameter of the bristle material of the brush seal 64 facilitates minimizing seal wear resulting from higher temperature at the rotary component-seal interface.

While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention. 

1. A rotary machine, comprising: a stationary component; a rotary component disposed inside the stationary component; and a brush sealing system disposed between the stationary component and the rotary component, comprising: a holding device coupled to the stationary component; and a plurality of carbon bristles, each bristle having a first end coupled to the holding device and a second end protruding from the holding device towards the rotary component; wherein diameter of each bristle is in the range of 0.1 to 1 mils.
 2. The rotary machine of claim 1, wherein the holding device comprises a first plate and a second plate configured to hold the plurality of bristles.
 3. The rotary machine of claim 2, wherein the first and second plates comprise a metallic material, a composite material, or a combination thereof.
 4. The rotary machine of claim 1, further comprising a matrix disposed between the first and second plates.
 5. The rotary machine of claim 4, wherein the first end of each bristle is coupled to the matrix disposed between the first and second plates.
 6. The rotary machine of claim 1, wherein strength of each bristle is at least 900 kilopounds per inch squared.
 7. The rotary machine of claim 1, wherein fiber modulus of each bristle is at least 19 megapounds per inch squared.
 8. The rotary machine of claim 1, wherein elongation of each bristle during operation of the rotary machine is 2 percent.
 9. The rotary machine of claim 1, wherein the second end of each bristle is configured to contact the rotary component to reduce leakage of pressurized fluid between the stationary component and the rotary component during operation of the machine.
 10. The rotary machine of claim 1, wherein the brush sealing system is coupled to a labyrinth sealing element recessed partially in the stationary component.
 11. The rotary machine of claim 1, wherein the rotary machine comprises an electric generator.
 12. The rotary machine of claim 1, wherein the rotary machine comprises a gas turbine.
 13. A brush sealing system, comprising: a holding device coupled to a stationary component; and a plurality of carbon bristles, each bristle having a first end coupled to the holding device, a second end protruding from the holding device towards a rotary component and configured to contact the rotary component to reduce leakage of pressurized fluid between the stationary component and the rotary component; wherein diameter of each bristle is in the range of 0.1 to 1 mils.
 14. The brush sealing system of claim 13, wherein the holding device comprises a first plate and a second plate configured to hold the plurality of bristles.
 15. The brush sealing system of claim 14, wherein the first and second plates comprise a metallic material, a composite material, or a combination thereof.
 16. The brush sealing system of claim 13, further comprising a matrix disposed between the first and second plates.
 17. The brush sealing system of claim 16, wherein the first end of each bristle is coupled to the matrix disposed between the first and second plates.
 18. The brush sealing system of claim 13, wherein strength of each bristle is at least 900 kilopounds per inch squared.
 19. The brush sealing system of claim 13, wherein fiber modulus of each bristle is at least 19 megapounds per inch squared.
 20. The brush sealing system of claim 13, wherein elongation of each bristle during rotation of the rotary component is 2 percent.
 21. A brush sealing system, comprising: a holding device coupled to a stationary component; and a plurality of carbon bristles, each bristle having a first end coupled to the holding device and a second end protruding from the holding device towards the rotary component; wherein each carbon bristle has friction coefficient less than or equal to 0.25, thermal conductivity greater than 8 watts per meter-kelvin, and temperature capability greater than 700 degrees fahrenheit.
 22. The brush sealing system of claim 21, wherein the holding device comprises a first plate and a second plate configured to hold the plurality of bristles.
 23. The brush sealing system of claim 22, further comprising a matrix disposed between the first and second plates.
 24. The brush sealing system of claim 23, wherein the first end of each bristle is coupled to the matrix disposed between the first and second plates.
 25. The brush sealing system of claim 21, wherein diameter of each bristle is in the range of 0.1 to 1 mils.
 26. The brush sealing system of claim 21, wherein the second end of each bristle is configured to contact a rotary component to reduce leakage of pressurized fluid between the stationary component and the rotary component.
 27. A method of operating a rotary machine, comprising: rotating a rotary component disposed inside a stationary component; and contacting a plurality of carbon bristles of a brush sealing system against the rotary component to reduce leakage of a pressurized fluid between the stationary component and the rotary component during operation of the machine; wherein diameter of each bristle is in the range of 0.1 to 1 mils.
 28. The method of claim 27, further comprising biasing the brush sealing system coupled to a labyrinth sealing element against the rotary component to reduce leakage of pressurized fluid between the stationary component and the rotary component during operation of the machine.
 29. The method of claim 28, further comprising biasing the brush sealing coupled to the labyrinth sealing element away from the rotary component during non-operating condition of the machine. 